Many, if not all, of Princess Catherine Radziwill's bitchy books can be found through Amazon or http://www.addall.com/. Some of her books have been reprinted as well.
She was also the subject of a biography, The Princess from St. Petersburg, published in August 2000 by the Book Guild.
Brian Robert wrote an excellent book, Cecil Rhodes and the Princess(Hamilton), which details the relationship between Rhodes and Princess Catherine. She was a very naughty girl.